Examples of currently used electrophotographic equipment which employs an electrophotographic process include copiers, printers, and facsimile machines. A photosensitive drum is generally incorporated into the electrophotographic equipment, and conductive rolls, such as a development roll, a charging roll, a transfer roll, and a toner feed roll, are arranged around the photosensitive drum.
As a development roll for electrophotographic equipment, rolls having various structures are used. For example, a development roll includes a shaft body, a rubber elastic layer disposed on the outer circumference of the shaft body, and a coating layer disposed on the outer circumference of the rubber elastic layer. For the purpose of securing a high toner-conveying capability so as to enhance image quality and the like, the surface of the development roll may be formed to have an irregular shape in some cases.
Examples of a method for forming the surface of a development roll so as to have an irregular shape include a method in which resin particles composed of a urethane resin or the like are dispersed in a coating layer, and a method in which, using a cylindrical mold having many concave portions on the inner circumferential surface thereof, an irregular shape is transfer-molded onto the surface of a rubber elastic layer.
For example, Japanese Unexamined Patent Application Publication No. 2009-186658 discloses a method for forming an irregular shape by transfer molding on the surface of a rubber elastic layer. A coating layer (intermediate layer) is disposed on the outer circumference of the rubber elastic layer, and a coating material containing a thermoplastic urethane, a polyol, and a curing agent is used in order to form the coating layer.
Since convex portions of a rubber elastic layer formed by transfer molding are soft, the convex portions are apt to be broken by friction between an opposing member, such as a layer-forming blade, and side surfaces (sloping surfaces) of the convex portions of the rubber elastic layer. For example, in a development roll of Japanese Unexamined Patent Application Publication No. 2009-186658, breakage of the convex portions of the rubber elastic layer is caused under endurance conditions.
When the convex portions of the rubber elastic layer are broken in such a manner, the rubber elastic layer is exposed at the roll surface, and in sections in which the rubber elastic layer is exposed at the surface, the rubber elastic layer comes into contact with a photosensitive member. When the rubber elastic layer and the photosensitive member are in contact with each other, the constituents of the rubber elastic layer, which have bled out to the exposed surface, may be moved on and contaminate the photosensitive member, resulting in image defects, which is a problem.